The invention relates to lifting rings, especially for heavy loads.
The lifting ring of the invention is more specifically intended for hanging loads requiring precise manoeuvres of positioning and orientation, such as industrial injection moulds, etc.
Conventional pivoting lifting rings comprise a pivoting body supporting a shackle and an anchor element consisting of a threaded rod.
Such rings are disclosed in particular in WO 90/10803 and GB 2 303 682.
Practice reveals that these rings raise a series of problems. Their weak point (rupture zone) is not usually the ring but the junction between the threaded part and the bearing face where the ring is placed against the load. This observation is found to be true with one-piece rings as well as articulated rings (it becomes worse if the ring is not perfectly in contact with the bearing face).
Besides this, users of tooling (particularly in the case of plastic injection moulds) often find the rings difficult to deal with as they leave little room for the lifting hook to be inserted, to such an extent that the various connectors, unions and pipelines become torn during handling, more especially when the handled parts are being turned over.
There is therefore a real need to safely increase the distance between the point of application of the hook and the surface of the moulds, but also a separate problem of safety, because very often users will resort to ad-hoc arrangements and other hazardous solutions with rings mounted on extension pieces to provide more distance between the point of application of the hook and the bearing face of the load.
The invention solves the above problems by providing rings with smooth shanks, with a retention system as set out in the technical report given below, and also makes possible, owing to the extra room achieved, the addition of a base whereby rings can have a large clearance combined with exceptional strength.
The subject of the invention is a lifting ring for a load, comprising a carrying loop, a pivoting body and an element that anchors in the body of a load in which the anchor element is a smooth cylindrical pin. A peripheral groove is formed near the free end of this pin, and an expandable retainer ring is inserted in said groove. The pin is engaged and locked axially in a cylindrical housing integral with the body of the load by the retainer ring. The cylindrical housing comprises a second peripheral groove opposite the groove in the pin, in which the expandable retainer ring is inserted.
The expandable retainer ring is preferably a split spring ring, or comprises a spring part exerting an outward force on rollers or segments so as to engage them in the channel.
The loop may be an integral part of the body of the ring. Alternatively it passes through an eye incorporated in the body of the ring.
In an advantageous embodiment, the cylindrical housing in which the pivoting body is mounted is formed in base fixed to the body of the load.
The top of this base may have a large clearance forwards of the surface of the load, thus facilitating hanging operations.
If so, it is advantageous to have the cylindrical housing pass through the base.
The cylindrical housing then advantageously comprises a section of larger diameter towards the back of the base, with an annular holder being inserted along this section, between the base and the pin, to keep the retainer ring or its components in place.
The pin may project beyond the back of the base into a cavity of corresponding diameter formed in the body of the load, thus improving its centring and its retention.
The invention also relates to a body for a lifting ring as described above, which comprises a loop, and a smooth cylindrical pin, a peripheral groove being formed near the free end of this pin and an expandable retainer ring being inserted in said groove.
A clamping collar advantageously keeps the retainer ring compressed and in position before the smooth pin is inserted in an appropriate housing.
One advantage of the invention is that the strength of the shank can be increased because, for example, a smooth pin with a diameter of 48 mm is stronger than an M 48 thread, especially at the junction with the ring. It is easy to increase strength by increasing the diameter from Ø 48 to Ø 56, which will increase the strength by about 1.8, thus offering a capacity for use in traction at 90xc2x0 close to that of axial traction. As a rule, the loss of efficiency at 90xc2x0 is of the order of 40% compared with axial traction, owing to the weakness at the point of junction with conventional rings in both one-piece and articulated designs.
The cost of a smooth shank Ø 56 is less than that of a threaded shank Ø 48, despite the smaller diameter.
Another advantage is that the invention solves the problem of tightening (or forgetting to tighten): a ring cannot only half snap or lock into position. Moreover, the capacity at the connection of the rod with the ring is reinforced.
The lifting ring according to the invention gives the manufacturer guaranteed values, corresponding to the drive for standardization, particularly from the major customers in the plastics industry, but also in other industries.